It is important in an automatic car wash that the control system have accurate information as to not only the width of the car but the precise location of the car sides such that uniform spacing between the spray head and the car sides can be maintained. A typical preferred spacing is approximately 14 inches. This will provide the most effective washing action and maintain clearance for side mounted accessories such as mirrors.
The most common prior art wash system does not attempt to determine the width of vehicles or to maintain uniform spacing between a treatment device and the sides of vehicles. Most prior art spray wash equipment washes vehicle sides with the spray nozzles at the same width for every vehicle. This nozzle position is usually wide enough to clear the widest vehicle expected. This approach leads to lower wash quality because the nozzles are too far away from medium and small vehicles.
Some wash systems used sensors that physically contacted the sides of vehicles. An example is a plastic rod attached to a mechanical limit switch. The rod would touch the vehicle, activating the switch. This could damage painted surfaces or get caught in mirrors or antennae or other parts.
Some other systems used photoelectric sensors, ultrasonic sensors, or other non-contact sensors. Some of these have worked incorrectly because they detected streams of spraying water as being the vehicle surface, or because they did not react consistently to the various angles and protrusions on vehicles. They also sometimes were not accurate or consistent in reading distances. Also, sunlight shining into a photoelectric receiver can sometimes activate the receiver, making it act as though it had received a signal from the photoelectric transmitter. Another problem with many photoelectric sensors, ultrasonic sensors, and other non-contact sensors is that they experience a high failure rate when subjected to large amounts of, or frequent exposure to, water.
The use of wheel sensors having electrical switches is shown in FIGS. 8 and 9. This wheel sensor determines when the vehicle has moved along the track to the desired position for the wash to begin. A treadleplate is depressed against the bias of a counter weight and a switch is closed sending a signal to a control system. The treadleplate extends laterally of the wheel line of travel. Information as to the relative lateral position of the wheel is not possible from this wheel sensor.
A wheel sensor in U.S. Pat. No. 4,178,948 determines the length of time a spray head will operate based on the duration of time the wheel is on the treadleplate which is determined by the width of the treadleplate. No information is provided as to the lateral positioning of the wheel or car side.
Thus, what is needed is a vehicle sizing sensor that will accurately and reliably determine the location of the vehicle sides such that a spray head can move along the sides with a uniform predetermined spacing.